Drainage and pressure relief vent for a sensor

ABSTRACT

A sensor is operably disposed within an environment containing a fluid including a sensing mechanism, a housing containing the sensing mechanism, a cavity intraposed between the sensing mechanism and the housing, and a vent for draining fluid from the cavity back to the environment.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to sensors for transaxles and,more particularly, to a drainage and pressure relief vent in a vehiclespeed sensor for a transaxle of a motor vehicle.

2. Description of the Related Art

Sensors are typically used in a variety of applications, including motorvehicles. The environment in which the vehicular sensor may be subjectto is also varied, and may involve temperature extremes, moisture, andfluids such as oils or fuels. The sensor may require protection from itsenvironment in order to preserve its functionality.

Motor vehicles, including those having front wheel drive or four wheeldrive transaxles, utilize an electromechanical speed sensor to providevehicle speed information for a speedometer system of the vehicle. For afront wheel drive motor vehicle, the vehicle speed sensor is mounted inan extension housing of the transaxle (a transmission mounted across theaxle), and for a four wheel drive motor vehicle, the vehicle speedsensor is mounted on a differential for the transaxle. The vehicle speedsensor is driven directly by a driveshaft of the transaxle, andgenerates a predetermined number of pulses per sensor shaft rotation.The vehicle speed sensor itself is protected by an external housing.There may be an empty space or cavity created between the vehicle speedsensor itself and the external housing. An example of a transaxle andvehicle speed sensor is disclosed in U.S. Pat. No. 4,875,391 to Leisinget al., the disclosure of which is hereby incorporated by reference.

The transaxle contains hydraulic fluid to lubricate and protect itsmoving parts. It is possible for hydraulic fluid to enter the vehiclespeed sensor through one or more possible locations: along a shaftbearing surface due to pumping or wicking action; along a lower externalhousing interface due to molding irregularities; and along an ultrasonicweld bonding an upper body portion to a lower body portion of theexternal housing. The hydraulic fluid that enters the vehicle speedsensor tends to accumulate in the cavities therein. This may result inseveral undesirable conditions: a fluid leak, fluid wicking into aconnector or wiring harness of the vehicle speed sensor and connectorsealing problems.

SUMMARY OF THE INVENTION

It is, therefore, one object of the present invention to provide adrainage and pressure relief vent for a sensor.

It is another object of the present invention to equalize differentialpressure between a fluid-filled cavity contained within a sensor and anexternal environment of the sensor.

It is yet another object of the present invention to provide for ventingof hydraulic fluid that has entered into a vehicle speed sensor mountedon a transaxle.

To achieve the foregoing objects, the present invention is a sensoroperably disposed within an environment containing a fluid including asensing mechanism and a housing containing the sensing mechanism. Thesensor also includes a cavity intraposed between the sensing mechanismand the housing and a vent for draining fluid from the cavity back tothe environment.

One advantage of the present invention is that a drainage and pressurerelief vent is provided for a sensor. Another advantage of the presentinvention is that the vent allows for draining of fluid that may haveaccumulated in a cavity of the sensor. Yet another advantage of thepresent invention is that the vent equalizes the differential pressurebetween the sensor and the sensor's external environment. A furtheradvantage of the present invention is that the vent improves theendurance and reliability of the sensor by eliminating fluid leaks,fluid wicking into the connector or wiring harness, and connectorsealing problems. A still further advantage of the present invention isthat the vent provides a simple, yet cost effective way of improving thereliability of the sensor.

Other objects, features and advantages of the present invention will bereadily appreciated as the same becomes better understood after readingthe subsequent description taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial fragmentary perspective view of a transaxle for amotor vehicle.

FIG. 2 is an elevational view of a vehicle speed sensor, according tothe present invention, mounted onto the transaxle of FIG. 1.

FIG. 3 is a fragmentary elevational view of the vehicle speed sensor ofFIG. 2.

FIG. 4 is a sectional view of a sensor body for the vehicle speed sensorof FIG. 3.

FIG. 5 is sectional view taken along line 5--5 of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring to FIG. 1, a transaxle 10 is shown for a motor vehicle such asan automotive vehicle (not shown). The transaxle 10 has a transmission11 which is preferably mounted east-west across an axle (not shown) ofthe vehicle, and converts engine torque and speed generated by apowerplant (not shown) into usable power to wheels of the vehicle forcontrolling movement of the vehicle. A vehicle speed sensor, accordingto the present invention and generally indicated at 12, is mounted ontoan extension housing 16 of the transaxle 10. It should be appreciatedthat the vehicle speed sensor 12 may also be mounted onto a differential(not shown but well known in the art) of the transaxle 10 for a fourwheel drive vehicle. It should also be appreciated that a signal fromthe vehicle speed sensor 12 provides an engine controller (not shown butwell known in the art) with vehicle speed information.

Referring to FIG. 2, the vehicle speed sensor 12 includes a sensor body,generally indicated at 18, having an upper body portion 20 and a lowerbody portion 22. The upper body portion 20 includes a connector portion23. The upper body portion 20 is joined to the lower body portion 22such as by ultrasonic welding and results in a weld joint 24therebetween. The sensor body 18 may be formed from metal, plastic orany other suitable material. It should be appreciated that ultrasonicwelding is one technique of joining the upper body portion 20 to thelower body portion 22 and that other suitable techniques may be used.

The vehicle speed sensor 12 includes a sensor shaft, generally indicatedat 25, operably attached to the sensor body 18. The sensor shaft 25 isdriven by an output or drive shaft of the transmission 11. The vehiclespeed sensor 12 generates a predetermined number of pulses per sensorshaft 25 rotation and sends a signal to a controller for processing asis known in the art.

Referring to FIG. 3, the vehicle speed sensor 12 includes a sensingmechanism, generally indicated at 26, which generates the predeterminednumber of pulses per sensor shaft rotation. The sensing mechanism 26 iswell known in the art and, for this example, includes a terminal pin 27and a batman assembly 28. The terminal pin 27 protrudes into a terminalconnector cavity 29 of the connector portion 23 from an upper portion ofthe batman assembly 28. The sensing mechanism 26 also includes a halleffect cell 30 affixed to a lower portion of the batman assembly 28.Adjacent to the hall effect cell 30, the sensing mechanism 26 includes aplurality of magnets 32 disposed in a hall effect cell cavity 34. Themagnets 32 surround a shaft 36 of the sensor shaft 25 which extendsaxially through the joined upper body portion 20 and lower body portion22. The upper end of the shaft 36 protrudes into the hall effect cellcavity 34. The sensor shaft 25 includes a bearing 37 surrounding theshaft 36. The bearing 37 is retained axially to the lower body portion22 by a flange interface 37a. It should be appreciated that the bearing37 rotates relative to the lower body portion 22. It should also beappreciated that the bearing 37 has a gear 37b that engages a gearportion (not shown) of an output shaft of the transmission 11.

Since the vehicle speed sensor 12 is installed in a location such as theextension housing 16 of the transaxle 10, it is subject to hydraulicfluid 38 normally contained within the transaxle 10. During vehicleoperation, the hall effect cell cavity 34 may become filled withhydraulic fluid 38. The hydraulic fluid 38 may enter the vehicle speedsensor 12 via several possible routes. For instance, hydraulic fluid 38may be pumped or wicked along a bearing surface 39 between the shaft 36and the bearing 37. The hydraulic fluid 38 may also enter the vehiclespeed sensor 12 at an interface 40 between the bearing 37 and the lowerbody portion 22 due to molding tolerances. The hydraulic fluid 38 mayfurther enter the vehicle speed sensor 12 at the ultrasonic weld joint24.

As the hall effect cavity 34 becomes filled with hydraulic fluid 38, andwith the addition of heat resulting from the operation of the vehicle,the hydraulic fluid 38 may be pushed out of the hall effect cell cavity34 along the batman assembly 28 and into the terminal connector cavity29, the void surrounding the terminal pin. 26. Another potential fluidpath is around the terminal strip and hall effect cell leads 42. Theseexamples of fluid paths are for illustration purposes, other fluid pathsare possible depending on the configuration of the sensing mechanism 26.

Hydraulic fluid 38 in the terminal connector cavity 29 is undesirablebecause it may result in several conditions, which may include a fluidleak from the vehicle speed sensor 12, fluid wicking into a connector orwiring harness (not shown) to be attached to the terminal pin 26, andconnector sealing problems. It should be appreciated that there is apositive pressure in the hall effect cell cavity 34 and a generallylower pressure or vacuum in the transaxle 10 where the vehicle speedsensor 12 is located.

Referring to FIGS. 3 through 5, the vehicle speed sensor 12 includes adrainage and pressure relief vent, generally indicated at 50, within thelower body portion 22 to equalize the differential pressures and allowthe hydraulic fluid 38 to drain back into the transaxle 10. The vent 50includes at least one, preferably a plurality of ducts 54 having anupper opening 52 communicating with the hall effect cell cavity 34 atone end and a lower opening 56 communicating with the external housing16 at the other end. As illustrated in FIG. 5, the lower body portion 22includes four ducts 54 having a diameter of approximately 0.080"-0.100"each. However, the number of ducts and size are for this particularexample.

As a result of the drainage and pressure relief vent 50, hydraulic fluid38 is allowed to drain back into the transaxle 10 and is prevented fromentering the terminal connector cavity 29. It should be appreciated thatthe number of ducts 54, size and shape will vary depending on theconfiguration of the vehicle speed sensor 10 and the potential for fluidflow into the vehicle speed sensor 10. It should also be appreciatedthat the drainage and vehicle speed pressure relief vent 50 can beimplemented in other types of sensors that may be subject to conditionswhere fluid may inadvertently flow into the sensor.

The present invention has been described in an illustrative manner. Itis to be understood that the terminology which has been used is intendedto be in the nature of words of description rather than of limitation.

Many modification and variations of the present invention are possiblein light of the above teachings. Therefore, within the scope of theappended claims, the present invention may be practiced otherwise thanas specifically described.

What is claimed is:
 1. A sensor operably connected to a fluid filledenvironment comprising:a sensing mechanism; a sensor housing containingsaid sensing mechanism; a cavity disposed within said sensor housingbetween said sensing mechanism and a portion of said sensor housing,whereby fluid from the environment has entered said cavity; and at leastone drainage and pressure relief vent within the portion of said sensorhousing and extending from said cavity through the portion of saidsensor housing for draining the fluid from said cavity through said atleast one drainage and pressure relief vent and into the environment asa differential pressure between the cavity and the environmentequalizes.
 2. A sensor as set forth in claim 1 wherein said at least onedrainage and pressure relief vent comprises at least one duct extendingfrom an upper opening in said cavity to a lower opening in said sensorhousing.
 3. A sensor as set forth in claim 1 wherein said sensor housingcomprises an upper body portion and a lower body portion welded to saidupper body portion.
 4. A sensor as set forth in claim 3 wherein said atleast one drainage and pressure relief vent comprises a plurality ofducts in said lower body portion and circumferentially disposedthereabout.
 5. A sensor as set forth in claim 4 wherein said pluralityof ducts comprises four ducts.
 6. A sensor as set forth in claim 1wherein said sensing mechanism is a vehicle speed sensor.
 7. A sensoroperably connected to a fluid filled member, comprising:a sensingmechanism; a sensor body having an upper body portion and a lower bodyportion surrounding said sensing mechanism; a cavity disposed withinsaid sensor body between said sensing mechanism and said upper and lowerbody portion of said sensor body, whereby fluid from the fluid filledmember has entered said cavity; and a drainage and pressure relief ventextending from said cavity through said lower body portion of saidsensor body for venting the fluid from said cavity through said vent andinto the member as a differential pressure between the cavity and themember equalizes.
 8. A sensor as set forth in claim 7 wherein said ventcomprises at least one duct extending from an upper opening in saidcavity to a lower opening in said housing.
 9. A sensor as set forth inclaim 7 wherein said vent comprises a plurality of ducts extending froman upper opening communicating with said cavity to a lower openingcommunicating with the member.
 10. A sensor as set forth in claim 9wherein said plurality of ducts comprises four ducts.
 11. A sensor asset forth in claim 7 wherein said sensing mechanism is a vehicle speedsensor.
 12. A vehicle speed sensor operably connected to a transaxlecontaining a fluid, comprising:a vehicle speed sensing mechanism; asensor body for containing said vehicle sensing mechanism having anupper body portion and a lower body portion; a cavity disposed withinsaid sensor body between said vehicle speed sensing mechanism and saidsensor body, whereby fluid from the transaxle has entered said cavity;and a plurality of passageways within the sensor body extending from anupper opening communicating with said cavity to a lower openingcommunicating with the transaxle, whereby a positive pressure within thecavity and a lower pressure within the transaxle creates a differentialpressure wherein the fluid passes from the cavity through the vent andinto the transaxle as the differential pressure equalizes.